This invention relates generally to a multipolar magnetic ring for generating a magnetic field with a sinusoidal form and whose period corresponds to one or more turns of the ring. More particularly, such a magnetic ring is to be associated with sensors of a magnetic type, notably absolute-position sensors used, for example, in sensor bearings.
Currently, multipolar magnetic rings are often used in applications of magnetic position sensors because of their simplicity of use and their low cost. Generally, the substrate of such multipolar magnetic rings consists of at least one magnetic phase, made of ferrite or rare earth metals, whose magnetic regions are oriented by magnetization so as to create north and south poles. This substrate may consist of two phases, one being magnetic as described above and the other being nonmagnetic, made of an elastomer, a polymer, or a heat-hardenable material, for example. This second configuration offers an excellent compromise between magnetic performance and manufacturing cost of the resulting magnetic ring.
The magnetization of a multipolar magnetic ring to obtain a succession of north and south poles can be carried out either pole by pole, using a magnetization head displaced over the magnetic substrate to be magnetized, or by creating all the poles simultaneously by means of a magnetizer with coiled wire. When the magnetic rings are associated with magnetic sensors of the probe type with a Hall effect device, or with magnetoresistance or variable reluctance devices, they generate sinusoidal electrical signals whose processing yields information on speed, direction of rotation, and relative position of the systems in which they are integrated.
FIG. 1a illustrates a circular magnetic ring with eight pairs of north and south poles, viewed axially, that, in association with a digital probe having a Hall effect device placed opposite the magnetic ring, delivers a periodic electric signal with a square form as represented in FIG. 1b. For a given number of pairs of north and south poles, a given type of magnetic material, a given magnetic ring geometry, a given magnetization technology, and a given pole width, the profile of the magnetic field, generated by the ring and sensed by the sensing element of an associated magnetic sensor, can be different.
FIGS. 2a through 2d represent examples of magnetic field profiles delivered by such magnetic rings, respectively, of a sinusoidal type corresponding to a sensor that is close to the ring, of a triangular type corresponding to a sensor that is at a greater distance from the ring, and of a truncated sinusoidal type. Only the first sinusoidal profile makes it possible to perform simple electronic interpolations to increase the resolution of the digital position sensors artificially. Consequently, these current multipolar magnetic rings only provide relative position information, not absolute position information, that is, completely unambiguous information on position as soon as voltage is applied, without an initialization step or a step searching for the reference position.
The foregoing illustrates limitations known to exist in present devices and methods. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.